wow… i have about 70% on my 2012 9cell and get about 2.5 hours with highly optimized config(slackware, power management, governor, brightness etc). 5-12hrs with a core2duo sounds very good.
still couldn’t find a proper new battery, hope i score one soon
i’ve kinda looked into it and my solution was running full libreoffice inside proot inside termux using termux-x11. kinda glitchy but it is surprisingly usable on a tablet+keyboard.